Embodiments relate to a light emitting device, a light emitting device package, and a lighting system.
Light emitting devices are compound semiconductor devices that convert electric energy into light energy. Light emitting devices may realize various colors by adjusting a composition ratio of a compound semiconductor.
When a forward voltage is applied into a light emitting device, the light emitting device emits light having energy corresponding to an energy gap between a conduction band and a valance band due to combination between electrons within an N-type layer and holes within a P-type layer. The energy may be mainly emitted in a heat or light state. Here, the light emitting device emits the energy in the light state.
For example, since a nitride semiconductor has high thermal stability and wide band gap energy, the nitride semiconductor comes into the spotlight in development fields of optical devices and high-output electronic devices. Specifically, blue, green, and ultraviolet (UV) light emitting devices using nitride semiconductors are commercialized, and are being widely used.
Light emitting devices may be classified into lateral type light emitting devices and vertical type light emitting devices according to positions of electrodes.
Specifically, a vertical type light emitting structure has a structure in which upper and lower electrodes are respectively disposed on upper and lower portions thereto and connected to each other. Thus, it may be unnecessary to perform a mesa etching process for connecting the electrodes to each other. Also, in the case of the vertical type light emitting structure, a reflective layer may be further disposed between a light emitting layer for emitting light and the lower electrode to improve light extraction efficiency.
The upper electrode disposed on the light emitting layer may have a minimum area to optimize the light extraction efficiency.
However, the upper electrode requires an electrode part (a pad electrode) having a pad shape and a wide area to stably connect a wire thereto. Also, an electrode part (a branch electrode) having a branch shape for supplying a power to an upper light emitting structure should have a predetermined area for improving a spreading effect.